code: def test_pipeline_add_at_start():
      def a(x):
          pass
  
      pipeline = (
          preprocessing.StandardScaler()
          | linear_model.LinearRegression()
      )
      pipeline = a | pipeline
      assert str(pipeline) == "a | StandardScaler | LinearRegression"
  
file_path: river/river/compose/test_.py
imports: from __future__ import annotations
  import pandas
  from river import compose, linear_model, preprocessing
label_desc: Use image node_id 2 for calling a global function with example usage: test_pipeline_add_at_start() without return types